摘要:

Hydrostatic pressure has been used as a tool in the study of creep in aluminun to show that there is a change of mechanism associated with the drop of activation energy for creep found as the temperature decreases below about 0.6Tm. Moreover, this change occurs, while the argument of the sinh (Ab&sgr;/kT) term in the usual lattice diffusion controlled theories of creep is still small with respect to one, i.e., before any sizeable vacancy supersaturation is build up.

ISSN:0021-8979    

DOI:10.1063/1.1657294

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The temperature dependence of the elastic constants of SnTe has been measured between 1.2 and 300 K. A change was found in the slope ofC44around 135 K in crystals with a carrier concentration of 6×1020carriers/cm3. No indication of a low temperature phase transition was seen. The 0°K Debye temperature for this carrier concentration is 192.2±0.4 K.

ISSN:0021-8979    

DOI:10.1063/1.1657295

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The formation of vacancy pits on the surface of electropolished aluminum on heating and subsequent cooling has been observed by several workers. The observations indicate that the formation of pits is a nucleation and growth process, and a minimum temperature drop &Dgr;Tis required in order to observe the pits. In the present work, a new technique has been developed to study this phenomenon. From a consideration of nucleation and growth of the pits, a relationship has been derived between &Dgr;TandThthe holding temperature. The relationship shows that &Dgr;Tdepends onThandp, the rate of cooling. &Dgr;TandThhave been measured experimentally and a value ofEm, the energy of migration of vacancies, has been evaluated on the basis of the relationship derived here. A value forEmof 0.6 eV is obtained for pure aluminium, which is in good agreement with the previously determined values ofEmin aluminium by other methods.

ISSN:0021-8979    

DOI:10.1063/1.1657296

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Ternary alloys of nickel‐palladium‐phosphorus and iron‐palladium‐phosphorus containing 15–20 at.% phosphorus were rapidly quenched from the liquid state. The structures of the quenched alloys were investigated by x‐ray diffraction. Broad maxima in the diffraction patterns, indicative of a glass‐like structure, were obtained for 13–73 at.% nickel and 13–44 at.% iron, with palladium and phosphorus adding up to 100%. The interference functions were evaluated from the coherent x‐ray scattering and used to compute the electronic radial distribution functions for these alloys. Average interatomic distances and coordination numbers were obtained from the radial distribution functions. A linear relationship between interatomic distances and composition, similar to Vegard's law in crystalline systems, was shown for these metallic glasses. The structure of the quenched Ni&sngbnd;Pd&sngbnd;P and Fe&sngbnd;Pd&sngbnd;P alloys could be explained in terms of structural units analogous to those existing in the metal‐rich phosphides. A quasi‐crystalline model based on the Pd3P structure, with nickel or iron substituting for palladium, was shown to give a very satisfactory approximation of the amorphous structure of the Ni&sngbnd;Pd&sngbnd;P and Fe&sngbnd;Pd&sngbnd;P alloys. Such a model was also in good agreement with electrical and magnetic properties measured for these metallic glasses.

ISSN:0021-8979    

DOI:10.1063/1.1657297

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Computer simulation and geometrical construction have been used to study the contrast from twin boundaries in field‐ion micrographs. For specific orientations of the twin boundary,mrings of (hkl) planes in the matrix are expected to match withnrings of (h′k′l′) planes in the twin, wheremandnare integers and (hkl) and (h′k′l′) are prominent planes in the matrix and the twin, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1657298

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The nonlinear absorption of ruby laser radiation by indanthrone dyes resulted in significant temporal shaping of the transmitted laser pulse at incident flux densities greater than 30 MW/cm2. This behavior and the observation that aggregation of the dye molecules is associated with the nonlinear response indicates that photochemical processes may be responsible for the effect. Models involving such processes were analyzed and the results compared to the experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1657299

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

We consider frequency‐doubling image conversion of a brilliant object by self‐interaction of its radiation within a nonlinear material. We have demonstrated that by placing the nonlinear material in the image plane of a lens, high‐resolution, three‐dimensional image conversion can be achieved, whereas for other positions of the nonlinear material crosstalk noise can be so severe as to make the resultant image unrecognizable. We have developed a theory of this type of image conversion which uses the formalism of Fourier optics. This theory is applied to a case which is very similar to more general image converters and this case is experimentally demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.1657300

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

It is shown that image upconversion using optically nonlinear materials is equivalent to a conventional hologram constructed at the signal wavelength and readout at the upconverted wavelength. As such, it should be a truly three‐dimensional, high‐resolution process. For the particular case of equal signal and pump wavelengths, the upconverted image will have only half the angular extent of the original object wave. The image's transverse dimensions remain unchanged while its location relative to the frequency doubler and its longitudinal dimensions double in size. It is also shown how the phase matching condition follows from the vector condition for the reconstruction of a thick hologram.

ISSN:0021-8979    

DOI:10.1063/1.1657301

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The decomposition of &ggr;‐Mn&sngbnd;Cu alloys containing more than 60 at.% Mn to the mixed (&agr;+&ggr;) phase has been studied using x‐ray and neutron diffractometry and measurements of electrical resistance and Young's modulus of elasticity. There is strong evidence that manganese‐enriched clusters having the &ggr;‐phase structure are produced prior to the precipitation of &agr;‐Mn. When &ggr;‐phase alloys were aged at 450°C for increasing periods of time, they remained single phase, but developed long‐range antiferromagnetic order associated with a tetragonal (c/a<1) lattice distortion, and with a corresponding rise of the Ne´el temperature to an asymptotic value of ∼470°K for all compositions. The effects of aging at other temperatures, and the behavior of furnace‐cooled alloys are discussed in terms of the pre‐precipitation of manganese‐rich clusters.

ISSN:0021-8979    

DOI:10.1063/1.1657302

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A method is described to deal with the problem of a rod (elliptical paraboloid) or a plate (parabolic cyclinder) growing uniformly in a matrix where the diffusion coefficient depends on concentration. As an example, the method is applied to the case where the diffusion coefficient has the formD=D0exp (A0C+A1C2), whereD0,A0, andA1are constants, andCis the concentration.

ISSN:0021-8979    

DOI:10.1063/1.1657303

出版商:AIP    

年代:1969

数据来源: AIP